Master Depth Of Field: The Ability You Can't Live Without

What You Should Know First

Before you can really understand the concept of depth field, you need to know that the a camera's lens are capable of focusing perfectly at a single lens-to-subject distance. This means that only one subject plane can ever be absolutely sharp at any one time.

In front or behind this plane of focus, all images are our of focus and the further away you move from the image plane, the image progessively become more out of focus.

However, the human eye's got a limited resolng power and that lead to a certain range of distances in front of and behind the plane og focus where the image still look acceptable sharp. This zone is called the depth of field.

Depth of field can range anywhere from millimeters (macro) to infinte distnaces, depending on a number of factors I will discuss later. As such, it is very important to you as a photographer, allowing you to focus attention on subjects by blurring or eliminating the background; or ensure sharp reproduction of fine details across vast distances.

Photo Sharing and Video Hosting at Photobucket

The Three Factors That Govern Depth Of Field

The Aperture, Focal Length And Distance

The aperture is the most powerful means to controlling depth of field. Unless you can easily change your aperture, you have very limited control over depth of field. The easiest way to vary aperture is of course through the Aperture Priority mode. The smaller the aperture (greater f/number) the greater the depth of field and vice versa.

The focal length of your camera is the second factor. The longer the focal length of your lens, the narrower the depth of field. As focal length increases, the zone of focus is reduced significantly due to increased magnification and this is why telephoto lenses has extremely shallow depth of field effects.

The last factor being the distance between your camera and the focal point. The closer you are to your focal point, the narrower the depth of field. This effect can be easily seen in macro photography where subjects are greatly magnified and can be centimeters away from the lens.

A subject near to the lens can lead to a very narrow depth of field.

Ensuring Depth Of Field Extends Precisely The Distance Across Your Subject

Minimizing Depth Of Field

This is no easy task. In fact, most of us wouldn't care to do this. But for those you want to try it out, here how you do it.

The first ways to do it is to use the depth of field and distance markings engraved on your lens barrel. Select your aperture and focus on your subject. Now record the distance values opposite the two markers indicating the aperture you are using. These are your nearest and farthest sharp points. Now you can vary your aperture and/or focusing distance to vary your depth of field. Most fixed lens feature depth of field markings.

The alternative is to use a depth of field tables for your lens. This is a list of maximum and minimum sharp focus points at all apertures over a wide range of subject distances. Almost all lenses feature distance scales on their barrels that the display the lens-to-subject distance whenever you focus.

How To Maxizimize Depth Of Field

Sometimes, you'll need to maximize your depth of field, such as shooting landscapes. It is crucial that everything from infinity to a close subject in the foreground is in sharp focus.

In this circumstance, use your widest focal length and a small aperture, making sure you use a tripod for stability.

The point your focus is of primary importance when you want to maximize depth of field. Focusing on the horizon will not maximize sharpness while focusing on the nearest foreground will blur the background. The distance that you should focus on is the Hyperfocal Distance.

When a lens is focused at the hyperfocal distance, depth of field stretches from half the hyperfocal distance to infinity. Therefore if your hyperfocal distance is 15 meters, depth of field will stretch from infinity to 7.5 meters in front of your camera.

Remember that the larger the aperture and the longer the focal length, the greater the hyperfocal distance. Therefore only short focal lengths used in conjunction with small aperture can ensure almost complete depth of field across near and far subjects.